Image processing device and method for operating endoscope system

ABSTRACT

A first signal ratio (−log(B/G)) between a B image signal and a G image signal is calculated. A second signal ratio (−log(G/R)) between the G image signal and an R image signal is calculated. A difference between first and second signal ratios in a first area and first and second signal ratios in a second area is increased to enhance a color difference between normal mucosa and an abnormal region (an atrophic mucosal region and a deep blood vessel region). An image after enhancing the color difference is displayed on a monitor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2014/057715 filed on Mar. 20, 2014, which claims priority under 35U. S. C. §119(a) to Japanese Patent Application No. 2013-066284, filedMar. 27, 2013 and Japanese Patent Application No. 2013-201274, filedSep. 27, 2013. Each of the above application(s) is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an image processing device forprocessing images used for diagnosing atrophic gastritis and a methodfor operating an endoscope system.

2. Description Related to the Prior Art

Diagnoses using endoscope systems have been widely performed in medicalfields. The endoscope system comprises a light source device, anelectronic endoscope, and a processor device. Due to high resolutionachieved by a high-definition imaging system such as an imaging element,which is to be incorporated in the endoscope, with high sensibility anda high number of pixels, recent models of the endoscope systems displayhigh resolution images that surpass the current image quality. Owing tothis, fine blood vessels and a small lesion in mucosa displayed lookextremely real.

Such high-definition imaging clarifies the shape and the size of alesion, facilitating the detection of the lesion. However, a doctorfinds a lesion based not only on the shape and the size of the lesionbut also on a slight difference in color between portions of mucosa. Forexample, a slightly reddish area that is slightly different in colorfrom the mucosa is detected as a lesion in its early stage. The slightlyreddish area may be overlooked only by increasing the resolution withthe use of the high-definition imaging.

In Japanese Patent No. 3228627, a color enhancement process is performedto enhance the redness of a reddish area and the whiteness of a whitearea in an image to prominently display a border between a normalportion and a lesion. The color enhancement process enables finding alesion which cannot be detected only by using the high-definitionimaging.

In recent years, a stomach lesion such as stomach cancer has beendetected based on a state of atrophic gastritis. The relationshipbetween the atrophic gastritis and the stomach lesion, which will bedescribed below, is used for the detection. As illustrated in a part (A)of FIG. 30, a surface mucosal layer of normal gastric mucosal structurehas certain thickness, so that the mucosal layer absorbs or reflectsmost of the light. For this reason, the blood vessels in the normalsubmucosal layer are hardly observed in an endoscopic image asillustrated in a part (B) of FIG. 30.

As illustrated in a part (A) of FIG. 31, in the case of gastric mucosalstructure in an advanced stage of the atrophic gastritis, the mucosallayer is thin due to decrease in gastric glandular cells. Changes ininternal structure of the gastric mucosa with the progress of theatrophic gastritis exhibit the following features (A) and (B) in anendoscopic image.

(A) The whitish color of muscularis mucosae is seen through the atrophicmucosa, so that the atrophic mucosal portion shows fading of color ascompared with the color of the normal portion.

(B) The blood vessels in the submucosal layer are seen through themucosal layer in the atrophic mucosal portion as the thickness of themucosal layer decreases with the progress of the atrophy (see a part (B)of FIG. 31). In diagnosing a gastric lesion based on the atrophicgastritis, the above-described two features (A) and (B) are used fordetermining staging of atrophy and a border between the normal portionand the portion with the gastritis.

In a case where the atrophy is in its advanced stage (for example, in acase where the atrophy is included in the group C or the group D in theABC screening), the above-described features (A) and (B) are clearlyobserved in the endoscopic image. However, in a case where the atrophyis in an intermediate stage (for example, in a case where the atrophy isincluded in the group B or the group C in the ABC screening), there islittle difference between the atrophic portion and the normal portion inthe endoscopic image, so that it may be difficult to determine thestaging of atrophy and the border between the normal portion and theportion with the gastritis. It is required to display the two features(A) and (B) clearly in the endoscopic image to clarify the borderbetween the normal portion and the portion with the gastritis.

The method described in the Japanese Patent No. 3228627 may be appliedto achieve the above. However, the method described in the JapanesePatent No. 3228627 enhances only the redness of a reddish area in animage and cannot enhance the changes in color of mucosa with theprogress of the atrophy of the stomach and cannot enhance and displaythe blood vessels that are located beneath the mucosa and seen throughthe mucosa as the atrophy progresses.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an image processingdevice that enhances changes in color of mucosa or the like in an imagedue to atrophy of stomach caused by atrophic gastritis and a method foroperating an endoscope system.

In order to achieve the above and other objects, an aspect of thepresent invention provides an image processing device comprising animage signal inputting unit, a signal ratio calculator, a colordifference enhancer, and a display unit. The image signal inputting unitinputs image signals of three colors. The signal ratio calculatorcalculates a first signal ratio between the image signals of two colorsand a second signal ratio between the image signals of two colorsdifferent from the first signal ratio, based on the image signals ofthree colors. The color difference enhancer performs a first expansionprocess for expanding a difference between first and second signalratios in a first area and first and second signal ratios in a secondarea different from the first area. The display unit displays an imagein which a color difference between normal mucosa and a first abnormalregion on an object of interest is enhanced based on the first andsecond signal ratios subjected to the first expansion process.

It is preferred that the first expansion process is a process forexpanding a radial coordinate difference between the first and secondsignal ratios in the first area and the first and second signal ratiosin the second area. It is preferred that the process for expanding theradial coordinate difference is performed based on a signal obtained bypolar coordinate conversion of the first and second signal ratios in thefirst area and a signal obtained by polar coordinate conversion of thefirst and second signal ratios in the second area. It is preferred thatsaturation of the first abnormal region is reduced by the firstexpansion process. It is preferred that the first abnormal region ismucosa showing fading of color, including atrophic mucosa. It ispreferred that the first expansion process expands the differencebetween the first and second signal ratios in the first area and thefirst and second signal ratios in the second area while the first andsecond signal ratios in the first area are maintained unchanged. It ispreferred that the display unit displays an image in which a color ofthe normal mucosa is maintained unchanged.

It is preferred that the color difference enhancer performs a secondexpansion process in addition to the first expansion process. The secondexpansion process expands a difference between the first and secondsignal ratios in the first area and first and second signal ratios in athird area different from the first and second areas. It is preferredthat the display unit displays an image in which the color differencebetween the normal mucosa and the first abnormal region on the object ofinterest and a color difference between the normal mucosa and a secondabnormal region on the object of interest are enhanced. It is preferredthat the second expansion process is a process for expanding an angularcoordinate difference between the first and second signal ratios in thefirst area and the first and second signal ratios in the third area. Itis preferred that the process for expanding the angular coordinatedifference is performed based on a signal obtained by polar coordinateconversion of the first and second signal ratios in the first area and asignal obtained by polar coordinate conversion of the first and secondsignal ratios in the third area. It is preferred that the secondabnormal region is located beneath the first abnormal region, and hue ofthe second abnormal region is changed by the second expansion process,so that blood vessels beneath the first abnormal region are seen throughthe first abnormal region. It is preferred that the second expansionprocess expands the difference between the first and second signalratios in the first area and the first and second signal ratios in thethird area while the first and second signal ratios in the first areaare maintained unchanged. It is preferred that the display unit displaysan image in which a color of the normal mucosa is maintained unchanged.

It is preferred that the image processing device further comprises anaverage value calculator for calculating an average value of the firstand second signal ratios in the first area. It is preferred that thecolor difference enhancer expands a difference between the average valueand the first and second signal ratios in the second area and expands adifference between the average value and the first and second signalratios in the third area. It is preferred that a suppression process forreducing the enhancement of the color difference is performed in a highluminance area or a low luminance area in the first to third areas. Itis preferred that the first signal ratio is a B/G ratio between a Bimage signal and a G image signal, and the second signal ratio is a G/Rratio between the G image signal and an R image signal.

An aspect of the present invention provides a method for operating anendoscope system comprising an image signal input step, a signal ratiocalculation step, a color difference enhancement step, and a displaystep. In the image signal input step, an image signal inputting unitinputs image signals of three colors. In the signal ratio calculationstep, a signal ratio calculator calculates a first signal ratio betweenthe image signals of two colors and a second signal ratio between theimage signals of two colors different from the first signal ratio, basedon the image signals of three colors. In the color differenceenhancement step, a color difference enhancer performs a first expansionprocess. The first expansion process expands a difference between firstand second signal ratios in a first area and first and second signalratios in a second area different from the first area. In the displaystep, a display unit displays an image in which a color differencebetween normal mucosa and a first abnormal region on an object ofinterest is enhanced based on the first and second signal ratiossubjected to the first expansion process.

According to an aspect of the present invention, the changes in color ofthe mucosa or the like in the image due to the atrophy of stomach causedby the atrophic gastritis are enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbe more apparent from the following detailed description of thepreferred embodiments when read in connection with the accompanieddrawings, wherein like reference numerals designate like orcorresponding parts throughout the several views, and wherein:

FIG. 1 is an external view of an endoscope system;

FIG. 2 is a block diagram illustrating functions of the endoscope of afirst embodiment;

FIG. 3 is a graph illustrating spectral intensity of white light;

FIG. 4 is a graph illustrating spectral intensity of special light;

FIG. 5 is a block diagram illustrating internal configuration of anabnormal region enhancer;

FIG. 6 is a graph illustrating a positional relationship among first tofifth areas;

FIG. 7 is a graph illustrating actual measurement data representingdistribution of first and second signal ratios obtained using thespecial light, in which the emission intensity of blue laser beams isgreater than the emission intensity of blue violet laser beams, forillumination;

FIG. 8 is an explanatory view illustrating positions of a second areaand a third area in a two-dimensional space (the vertical axis: -log(B/G), the horizontal axis:-log(G/R)) before a color differenceenhancement process;

FIG. 9 is an explanatory view illustrating positions of the second areaand the third area in the two-dimensional space after the colordifference enhancement process;

FIG. 10 is an explanatory view illustrating changes in distribution ofthe first and second signal ratios with the progress of atrophicgastritis and a relationship between the two-dimensional space andchromaticity;

FIG. 11 is a flowchart illustrating steps in diagnosing the atrophicgastritis;

FIG. 12 is an explanatory view illustrating a positional relationshipbetween a first area and each of second to fifth areas, for the casewhere the special light including the blue narrowband light is used, anda positional relationship between the first area and each of second tofifth areas, for the case where the illumination light including theblue broadband light is used, in a two-dimensional space;

FIG. 13 is a graph illustrating a relationship between reflectiondensity, and absorption coefficient and distribution density of a lightabsorbing material;

FIG. 14 is a graph illustrating distribution of absorption coefficientof hemoglobin;

FIG. 15 is a graph illustrating distribution of reflection density of aBA (brownish area) region;

FIG. 16 is an explanatory view illustrating the BA region, in whichblood density in mucosal layer is locally high in a surface layer;

FIG. 17 is an explanatory view illustrating a positional relationship ina two-dimensional space between the fourth area, for the case wherenarrowband B light is used, and the fourth area for the case wherebroadband B light is used;

FIG. 18 is a graph illustrating distribution of reflection density of aredness region;

FIG. 19 is an explanatory view illustrating the redness region, in whichthe blood density in the mucosal layer is locally high across themucosa;

FIG. 20 is an explanatory view illustrating a positional relationship ina two-dimensional space between the fifth area, for the case where thenarrowband B light is used, and the fifth area for the case where thebroadband B light is used;

FIG. 21 is a block diagram illustrating functions of an endoscope systemof a second embodiment;

FIG. 22 is a plan view illustrating a rotary filter;

FIG. 23 is a block diagram illustrating functions of a special lightimage processor of a third embodiment;

FIG. 24 is an explanatory view illustrating a radial coordinate of thefirst area, a radial coordinate of the second area, and a radialcoordinate of the third area;

FIG. 25 is an explanatory view illustrating a radial coordinate of thefirst area, a radial coordinate of the fourth area, and a radialcoordinate of the fifth area;

FIG. 26 is a graph illustrating a relationship between radial coordinater and radial coordinate Er;

FIG. 27 is an explanatory view illustrating an angular coordinate of thefirst area, an angular coordinate of the second area, and an angularcoordinate of the third area;

FIG. 28 is an explanatory view illustrating an angular coordinate of thefirst area, an angular coordinate of the fourth area, and an angularcoordinate of the fifth area;

FIG. 29 is a graph illustrating a relationship between the angularcoordinate θ and the angular coordinate Eθ;

A part (A) of FIG. 30 is a cross-sectional view of a mucosal structureof normal mucosa and a part (B) of FIG. 30 is a plan view of the normalmucosa viewed from a surface layer side;

Apart (A) of FIG. 31 is a cross-sectional view of a mucosal structurewith the atrophic gastritis in which the thickness of gastric mucosallayer is reduced due to decrease in glandular cells of stomach orsubstitution of intestinal tissue or fibrous tissue for stomach tissue,and a part (B) of FIG. 31 is a plan view of mucosa with the atrophicgastritis viewed from the surface layer side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

In FIG. 1, an endoscope system 10 according to a first embodimentcomprises an endoscope 12, a light source device 14, a processor device16, a monitor 18, and a console 20. The endoscope 12 is connectedoptically to the light source device 14 and electrically to theprocessor device 16. The endoscope 12 comprises an insertion section 21to be inserted into a body cavity, a control handle unit 22 provided atthe proximal end of the insertion section 21, a flexible portion 23, anda distal portion 24. The flexible portion 23 and the distal portion 24are provided on the distal side of the insertion section 21. Theflexible portion 23 is bent by operating an angle knob 22 a of thecontrol handle unit 22. The distal portion 24 is directed to a desireddirection by bending the flexible portion 23.

The control handle unit 22 is provided with the angle knob 22 a, a modeswitch (SW) 22 b, and a zoom operating section 22 c. The mode SW 22 b isoperated to switch between two observation modes: a normal observationmode and a special observation mode. In the normal observation mode, abody cavity is irradiated with white light. In the special observationmode, the body cavity is irradiated with special light of a bluishcolor, and the changes in colors of mucosa and blood vessels seenthrough the mucosa that may occur due to the atrophy of stomach causedby atrophic gastritis are enhanced. The zoom operating section 22 cdrives a zooming lens 47 (see FIG. 2), which is provided in theendoscope 12, to magnify an object. Note that in the special observationmode, the white light may be used instead of the special light.

The processor device 16 is electrically connected to the monitor 18 andthe console 20. The monitor 18 outputs and displays image informationand the like. The console 20 functions as a UI (user interface), whichreceives input operation such as setting a function. Note that anexternal storage unit (not shown) for recording the image informationand the like may be connected to the processor device 16.

As illustrated in FIG. 2, the light source device 14 comprises a bluelaser (445LD) 34 and a blue violet laser (405LD) 36, being the lightsources. The blue laser (445LD) 34 emits blue laser beams having thecenter wavelength 445 nm. The blue violet laser (405LD) 36 emits blueviolet laser beams having the center wavelength 405 nm. The lightemissions from the semiconductor light emitting elements of each of thelasers 34 and 36 are controlled independently by a source controller 40.A light quantity ratio between the light from the blue laser 34 and thelight from the blue violet laser 36 is changed as desired. In the normalobservation mode, the source controller 40 actuates the blue laser 34,mostly, and controls the blue laser 34 to allow slight emission of theblue violet laser beams. Note that the blue violet laser 36 may beactuated in the normal observation mode. In this case, it is preferredto maintain the emission intensity of the blue violet laser 36 at a lowlevel.

In the special observation mode, both of the blue laser 34 and the blueviolet laser 36 are actuated. The light emission ratio is controlledsuch that the light emission ratio of the blue laser beams is greaterthan that of the blue violet laser beams. Note that it is preferred thatthe full width at half maximum of the blue laser beams or theblue-violet laser beams is in the order of ±10 nm. Broad-area typeInGaN-based laser diodes, InGaNAs-based laser diodes, or GaNAs-basedlaser diodes may be used as the blue laser 34 and the blue-violet laser36. A light emitting element such as a light emitting diode may be usedas the light source.

The laser beams from each of the lasers 34 and 36 enter a light guide(LG) 41 through optical members such as a condenser lens, an opticalfiber, a combiner, and the like (all not shown). The light guide 41 isincorporated in the light source device 14, the endoscope 12, and auniversal cord (a cord for connecting the endoscope 12 to the lightsource device, not shown). The blue laser beams having the centerwavelength of 445 nm or the blue violet laser beams having the centerwavelength of 405 nm are transmitted to the distal portion 24 of theendoscope 12 through the light guide 41. Note that a multimode fiber maybe used as the light guide 41. For example, a small-diameter fiber cablewith the core diameter 105 μm, the clad diameter 125 μm, and the outerdiameter φ 0.3 to 0.5 mm (including a protection layer, being a jacket)may be used.

The distal portion 24 of the endoscope 12 comprises an illuminationoptical system 24 a and an imaging optical system 24 b. The illuminationoptical system 24 a comprises phosphor 44 and a light lens 45. The bluelaser beams having the center wavelength 445 nm or the blue violet laserbeams having the center wavelength 405 nm, which are transmitted throughthe light guide 41, are incident on the phosphor 44. The phosphor 44irradiated with the blue laser beams emits fluorescence. A part of theblue laser beams pass through the phosphor 44. The blue-violet laserbeams pass through the phosphor 44 without exciting the phosphor 44. Thelight emanating from the phosphor 44 is applied to the object throughthe light lens 45.

Here, in the normal observation mode, the blue laser beams are mostlyincident on the phosphor 44, so that the white light, being thecombination of the blue laser beams and the fluorescence from thephosphor 44 excited by the blue laser beams as illustrated in FIG. 3, isapplied to the body cavity. In the special observation mode, both theblue-violet laser beams and the blue laser beams are incident on thephosphor 44, so that the special light, being the combination of theblue-violet laser beams, the blue laser beams, and the fluorescence fromthe phosphor 44 excited by the blue laser beams as illustrated in FIG.4, is applied to the body cavity. In the special observation mode, thespecial light is broadband light that includes a high amount of bluecomponent and the wavelength of which covers substantially the entirevisible range because the special light includes the blue violet laserbeams in addition to the blue laser beams, in which the light emissionintensity of the blue component is high.

Note that it is preferred to use the phosphor 44 containing two or moretypes of phosphor (e.g. YAG-based phosphor, BAM(BaMgAl₁₀O₁₇), or thelike) that absorb a part of the blue laser beams and emit light of greento yellow colors. In the case where the semiconductor light emittingelements are used as the excitation light sources for the phosphor 44 asdescribed in this example, the high-intensity white light is providedwith high light-emission efficiency, the intensity of the white light iscontrolled easily, and the variations in the color temperature andchromaticity of the white light are maintained at a low level.

As illustrated in FIG. 2, the imaging optical system 24 b of theendoscope 12 has a taking lens 46, the zooming lens 47, and an imagesensor 48. The light reflected from the object is incident on the imagesensor 48 through the taking lens 46 and the zooming lens 47. Thereby areflection image of the object is formed on the image sensor 48.Operating the zoom operating section 22 c moves the zooming lens 47between the telephoto end and the wide angle. The size of the reflectionimage of the object is reduced when the zooming lens 47 is moved to thewide angle end side. The size of the reflection image of the object ismagnified when the zooming lens is moved to the telephoto end side.

The image sensor 48 is a color image sensor, which captures thereflection image of the object and outputs image signals. Note that itis preferred that the image sensor 48 is a CCD (Charge Coupled Device)image sensor, a CMOS (Complementary Metal-Oxide Semiconductor) imagesensor, or the like. The image sensor used in the present invention isan RGB image sensor having RGB channels (ch) and provided with RGB colorfilters on an imaging plane. Photoelectric conversion is performed foreach channel. Thereby an R image signal is outputted from an R pixelprovided with an R (red) color filter. A G image signal is outputtedfrom a G pixel provided with a G (green) color filter. A B image signalis outputted from a B pixel provided with a B (blue) color filter.

Note that the image sensor 48 may be an image sensor comprising CMYGfilters (C: cyan, M: magenta, Y: yellow, and G: green) on the imagingplane. In the case where the image sensor with the CMYG filters is used,CMYG image signals of four colors are converted into the RGB imagesignals of three colors. In this case, it is necessary that one of theendoscope 12, the light source device 14, and the processor device 16comprises a color conversion means for converting the CMYG image signalsof four colors into the RGB image signals of three colors.

The image signal outputted from the image sensor 48 is transmitted to aCDS/AGC circuit 50. The CDS/AGC circuit 50 performs correlated doublesampling (CDS) and automatic gain control (AGC) on the image signal thatis an analog signal. A gamma converter 51 performs gamma conversion onthe image signal that has passed through the CDS/AGC circuit 50. Therebyan image signal having a tone suitable for an output device (e.g. themonitor 18) is generated. After the gamma conversion, an A/D converter52 converts the image signal into a digital image signal. The A/Dconverted digital image signal is inputted to the processor device 16.

The processor device 16 comprises a receiver 54, an image processingselector 60, a normal light image processing unit 62, a special lightimage processing unit 64, and an image display signal generator 66. Thereceiver 54 receives digital image signals from the endoscope 12. Thereceiver 54 comprises a DSP (Digital Signal Processor) 56 and a noiseremover 58. The DSP 56 performs gamma correction and color correction onthe digital image signals. The noise remover 58 removes noise from thedigital image signals that have been subjected to the gamma correctionand the like performed by the DSP 56, through a noise removing process(for example, moving average method or median filter method). Thedigital image signals from which the noise has been removed aretransmitted to the image processing selector 60. Note that the “imagesignal inputting unit” of the present invention corresponds to theconfiguration that includes the receiver 54, for example.

In a case where the mode is set to the normal observation mode with theuse of the mode SW 22 b, the image processing selector 60 transmits thedigital image signals to the normal light image processing unit 62. In acase where the mode is set to the special observation mode, the imageprocessing selector 60 transmits the digital image signals to thespecial light image processing unit 64.

The normal light image processing unit 62 comprises a color converter68, a color enhancer 70, and a structure enhancer 72. The colorconverter 68 assigns the inputted digital image signals of threechannels (RGB) to R image data, G image data, B image data,respectively. The RGB image data is converted into color-converted RGBimage data by a color conversion process such as 3×3 matrix processing,a tone conversion process, or a three-dimensional LUT process.

The color enhancer 70 performs various types of color enhancementprocesses on the color-converted RGB image data. The structure enhancer72 performs a structure enhancement process (spatial frequencyenhancement or the like) on the color-enhanced RGB image data. The RGBimage data that has been subjected to the structure enhancement processperformed by the structure enhancer 72 is inputted as the normal lightimage from the normal light image processing unit 62 to the imagedisplay signal generator 66.

The special light image processing unit 64 has an inverse gammaconverter 76, an abnormal region enhancer 77, and a structure enhancer78. The inverse gamma converter 76 performs inverse gamma conversion onthe digital image signals of three channels (RGB) inputted. Since theRGB image signals after the inverse gamma conversion arereflectance-linear RGB signals, which change linearly relative to thereflectance from the object, the reflectance-linear RGB signals containa high amount of various types of biological information (in thisembodiment, information about the atrophy of stomach such as changes incolor of the stomach caused by the atrophic gastritis) of the object.

Based on the reflectance-linear RGB image signals, the abnormal regionenhancer 77 performs a color difference enhancement process forenhancing a difference in color between a normal mucosal region and anabnormal region, which may contain a lesion such as stomach cancer. Thedetails of the abnormal region enhancer 77 will be described below. Thestructure enhancer 78 performs the structure enhancement process such asthe spatial frequency enhancement on the RGB image data that has beensubjected to the color difference enhancement process. The RGB imagedata that has been subjected to the structure enhancement processperformed by the structure enhancer 78 is inputted as the special lightimage from the special light image processing unit 64 to the imagedisplay signal generator 66.

The image display signal generator 66 converts the normal light image,which is inputted from the normal light image processing unit 62, or thespecial light image, which is inputted from the special light imageprocessing unit 64, into a display image signal, which is to bedisplayed as a displayable image on the monitor 18. Based on the displayimage signal after the conversion, the monitor 18 displays the normallight image or the special light image.

As illustrated in FIG. 5, the abnormal region enhancer 77 comprises asignal ratio calculator 80, a color difference enhancer 82, an RGBconverter 83, and a gamma converter 84. The signal ratio calculator 80calculates a first signal ratio (−log(B/G)) between the B signal and theG signal of the reflectance-linear RGB signals and a second signal ratio(−log(G/R)) between the G signal and the R signal of thereflectance-linear RGB signals. The first and second signal ratios arenormalized by the G and R signals, respectively, so that a distance fromthe object of interest and brightness of an observation area have littleinfluence on the first and second signal ratios. However, the first andsecond signal ratios fluctuate significantly with a change in thedensity of the light absorbing components or a change in the internalmucosal structure because the first and second signal ratios contain theB and G signals, respectively, which correlate with a change in thedensity of the light absorbing components (hemoglobin) in mucosa, achange in the internal mucosal structure, or the like. Note that theabove-described B signal corresponds to the B image signal outputtedfrom the B pixel of the image sensor 48. The above-described G signalcorresponds to the G image signal outputted from the G pixel of theimage sensor 48. The above-described R signal corresponds to the R imagesignal outputted from the R pixel of the image sensor 48.

For example, the first signal ratio correlates with the depth of bloodvessels (the position of the blood vessels in the depth direction of themucosa), so that the first signal ratio of a portion with large bloodvessels such as deep-layer blood vessels increases as the depth of theblood vessels increases and decreases as the depth of the blood vesselsdecreases. Both of the first signal ratio and the second signal ratiocorrelate with the absorption of hemoglobin, so that the first andsecond signal ratios increase as the absorption of light increases.

The signal ratio calculator 80 comprises a high/low luminance areadeterminer 80 a for determining the high luminance area and the lowluminance area in the reflectance-linear RGB signals. In the highluminance area, the luminance value is greater than or equal to an upperlimit value. In the low luminance area, the luminance value is less thanor equal to a lower limit value. The high and low luminance areasinclude significant noise. In a case where the first or second signalratio is calculated using signals in the high or low luminance area, thefirst or second signal ratio may take an extremely large value,enhancing the noise. For this reason, a level of the enhancement processfor an area determined as the high or low luminance area by the high/lowluminance area determiner 80 a is suppressed (suppression process), ascompared with the level of the enhancement process for another area,which will be described below. Note that the R signal of thereflectance-linear RGB signals varies in association with the amount ofreflection light. Therefore it is preferred to determine the high andlow luminance areas based on the R signal.

The color difference enhancer 82 comprises an average value calculator82 a, an atrophic mucosal region enhancer 82 b, a deep blood vesselregion enhancer 82 c, a BA region enhancer 82 d, and a redness regionenhancer 82 e. The color difference enhancer 82 increases a differencebetween the first and second signal ratios in the first area and thefirst and second signal ratios in each of the second to fifth areas inthe two-dimensional space (the vertical axis: the first signal ratio(-log(B/G), the horizontal axis: the second signal ratio (-log(G/R))shown in FIG. 6, to increase a color difference between the normalmucosa and an abnormal region (the atrophic mucosa, BA (Brownish area),redness, or the like) in the observation area.

The actual measurement data shown in FIG. 7 indicates that the firstarea mostly contains the first and second signal ratios corresponding tothe normal mucosa. In FIG. 7, “∘” denotes the normal mucosa. The firstarea is located substantially at the center in the two-dimensionalspace. The second area mostly contains the first and second signalratios corresponding to the atrophic mucosa. In FIG. 7, “×” denotes theatrophic mucosa. The second area is located at the lower left of thefirst area in the two-dimensional space. The third area mostly containsthe first and second signal ratios corresponding to deep blood vessels.In FIG. 7, “□” denotes the deep blood vessels. The third area is locatedat the lower right of the first area. The fourth area mostly containsthe first and second signal ratios corresponding to BA. In FIG. 7, “⋄”denotes the BA. The fourth area is located at the upper right of thefirst area. The fifth area mostly contains the first and second signalratios corresponding to redness. In FIG. 7, “Δ” denotes the redness. Thefifth area is located to the right of the first area.

The average value calculator 82 a calculates the average value of thefirst and second signal ratios in the first area. The average valuecalculator 82 a performs polar coordinate conversion of the calculatedaverage value to obtain a first area average value (rm, θm) that hasbeen subjected to the polar coordinate conversion.

The atrophic mucosal region enhancer 82 b performs polar coordinateconversion of the first and second signal ratios in the second area toobtain a second area signal (ri, θi) that has been subjected to thepolar coordinate conversion. The atrophic mucosal region enhancer 82 bperforms a first expansion process for expanding (increasing) a radialcoordinate difference Δr between the first area average value (rm, θm)and the second area signal (ri, θi), which have been subjected to thepolar coordinate conversion, as illustrated in FIG. 8. The firstexpansion process is performed using an expression (1) shown below.Thereby an enhanced second area signal (Eri, θi) is obtained. Asillustrated in FIG. 9, a radial coordinate difference EΔr between theenhanced second area signal (Eri, θi) and the first area average value(rm, θm) is greater than Δr.

Eri=(ri−rm)·α+rm(α≧1)   (1)

As illustrated in FIGS. 8 and 9, the atrophic mucosal region enhancer 82b performs the first expansion process to expand the radial coordinatedifference Δr in a direction to reduce the saturation while maintainingthe hue unchanged. The color is changed through the first expansionprocess in accordance with the change in the color of mucosa fading withthe progress of the atrophic gastritis as illustrated in FIG. 10. InFIG. 10, stage 2 means that the atrophic gastritis is more advanced thanthat at stage 1. The difference between the atrophic mucosal region andthe normal mucosal region is small at the stage 1. At the stage 2, onthe other hand, the difference between the atrophic mucosal region andthe normal mucosal region is increased by reducing only the saturationwhile the hue is maintained unchanged.

In the special light image displayed on the monitor 18 based on theenhanced second area signal (Eri, θi), the atrophic mucosal regionclearly appears in colors different from those of the normal mucosalregion and the color of the atrophic mucosal region is substantially thesame as the actual color of the mucosa with the atrophic gastritis.Thereby the border between the normal mucosal region and the atrophicmucosal region is determined reliably. The first expansion process isespecially effective for the cases where a color difference between thenormal mucosal region and the atrophic mucosal region is small (forexample, for the cases where the atrophic gastritis is progressing,corresponding to the group B or the group C of the ABC screening).

Note that the expansion in the hue direction (the expansion of anangular coordinate difference) may be performed in addition to theexpansion in the saturation direction (the expansion of a radialcoordinate difference) to further enhance the difference in colorbetween the normal mucosal region and the atrophic mucosal region. Theexpansion is suppressed by reducing the value a in the high and lowluminance areas (suppression process). In a case where the atrophy is ina highly advanced stage, the color of the atrophic mucosal regionbecomes bluish when the value α in the expression (1) is too large. Inthis case, the value a is reduced (the value α is adjusted by operatingthe console 20) to make the color of the atrophic mucosal region thesame as the actual color (the faded color) of the atrophic mucosa.

The deep blood vessel region enhancer 82 c performs the polar coordinateconversion of the first and second signal ratios in the third area toobtain a third area signal (rv, θv) that has been subjected to the polarcoordinate conversion, and performs a second expansion process forexpanding (increasing) an angular coordinate difference A between thefirst area average value (rm, θm) and the third area signal (rv, θv),which have been subjected to the polar coordinate conversion (see FIG.8). The second expansion process is performed using an expression (2)shown below. Thereby an enhanced third area signal (rv, Eθv) isobtained. As illustrated in FIG. 9, an angular coordinate difference EΔθbetween the enhanced third area signal (rv, Eθv) and the first areaaverage value (rm, θm) is greater than Δθ.

Eθv=(θv−θm)·β+θm(β≧1)   (2)

As illustrated in FIGS. 8 and 9, the second expansion process performedby the deep blood vessel region enhancer 82 c is to expand the angularcoordinate difference Δθ in the hue direction while the saturation ismaintained unchanged. The color is changed through the second expansionprocess in accordance with the change in the color of the deep bloodvessels becoming more apparent as the atrophic gastritis progresses asillustrated in FIG. 10. In FIG. 10, the stage 2 means that the atrophicgastritis is at a more advanced stage than the stage 1. The differencebetween the atrophic mucosal region and the normal mucosal region issmall at the stage 1. At the stage 2, on the other hand, the differencebetween the atrophic mucosal region and the normal mucosal region isincreased by changing only the hue while the saturation is maintainedsubstantially unchanged.

Thereby, the special light image that is displayed on the monitor 18based on the enhanced third area signal (rv, Eθv) clearly shows the deepblood vessel region in colors that differ from those of the normalmucosal region. Because the colors of the deep blood vessels areapparent in the special light image, the deep blood vessels are seenpositively through the atrophic mucosa. Thus, the border between thenormal mucosal region and the deep blood vessel region is determinedreliably. The second expansion process is especially effective for thecases where the deep blood vessels are not clearly seen through theatrophic mucosa (for example, for the cases where the atrophy isprogressing, corresponding to the group B or the group C of the ABCscreening).

Note that the expansion in the saturation direction (the expansion ofthe radial coordinate difference) may be performed in addition to theexpansion in the hue direction (the expansion of the angular coordinatedifference) to further enhance the difference in color between thenormal mucosal region and the deep blood vessel region. With regard tothe high and low luminance areas, the value β is reduced to suppress theexpansion (suppression process). In a case where the atrophy is highlyprogressed, the color of the deep blood vessel region is magenta-tintedif the value β of the expression (2) is too large. In this case, thevalue β is reduced (the value a is adjusted by operating the console 20)to make the color of the deep blood vessel region the same as the actualcolor of the deep blood vessels.

The BA region enhancer 82 d performs the polar coordinate conversion ofthe first and second signal ratios in the fourth area, to obtain afourth area signal (rk, θk) that has been subjected to the polarcoordinate conversion. The BA region enhancer 82 d performs a thirdexpansion process with the use of expressions (3) and (4) shown below.The third expansion process expands (increases) the radial coordinatedifference Δr and the angular coordinate difference Δθ between the firstarea average value (rm, θm) and the fourth area signal (rk, θk) thathave been subjected to the polar coordinate conversion. Thereby, anenhanced fourth area signal (Erk, Eθk) in which both of the radialcoordinate difference Δr and the angular coordinate difference Δθ areexpanded is obtained.

Erk=(rk−rm)·α+rm(α≧1)   (3)

Eθk=(θk−θm)·β+θm(β≧1)   (4)

A special light image displayed on the monitor 18 based on the enhancedfourth area signal (Erk, Eθk) clearly shows the BA region in colors thatdiffer from those of the normal mucosal region. Thereby the borderbetween the normal mucosal region and the BA region is determinedreliably. Note that the BA region enhancer 82 d may expand one of theradial coordinate difference Δr and the angular coordinate differenceΔrθ, instead of increasing both of the radial coordinate difference Δrand the angular coordinate difference A. The values α and β for the highand low luminance areas are reduced to suppress the expansion(suppression process).

The redness region enhancer 82 e performs the polar coordinateconversion of the first and second signal ratios in the fifth area, toobtain a fifth area signal (rj, θj) that has been subjected to the polarcoordinate conversion. The redness region enhancer 82 e performs afourth expansion process with the use of expressions (5) and (6) shownbelow. The fourth expansion process expands (increases) the radialcoordinate difference Δr and the angular coordinate difference Δθbetween the first area average value (rm, θm) and the fifth area signal(rj, θj) that have been subjected to the polar coordinate conversion.Thereby an enhanced fifth area signal (Erj, Eθj) in which both of theradial coordinate difference Δr and the angular coordinate difference Δθare expanded is obtained.

Erj=(rj−rm)·α+rm(α≧1)   5)

Eθj=(θj−θm)·β+θm(β≧1)   (6)

A special light image displayed on the monitor 18 based on the enhancedfifth area signal (Erj, Eθj) clearly shows the redness region in colorsthat differ from those of the normal mucosal region. Thereby, the borderbetween the normal mucosal region and the redness region is determinedreliably. Note that the redness region enhancer 82 e may increase one ofthe radial coordinate difference Δr and the angular coordinatedifference Δθ, instead of increasing both of the radial coordinatedifference Δr and the angular coordinate difference Δθ. The values α andβ for the high and low luminance areas are reduced to suppress theexpansion (suppression process).

The RGB converter 83 converts the enhanced color difference signal (theenhanced atrophic mucosa signal, the enhanced deep blood vessel signal,the enhanced BA signal, and the enhanced redness signal), which aregenerated by the color difference enhancer 82, back into the RGB imagedata. The RGB converter 83 converts the enhanced color differencesignal, which represents a value in a polar coordinate space, back intothe RGB values. The gamma converter 84 performs the gamma conversion onthe RGB image data whose color difference has been enhanced. Thereby thecolor-difference-enhanced RGB image data having the tone suitable for anoutput device such as the monitor 18 is generated.

Hereinafter, referring to a flowchart in FIG. 11, steps of thisembodiment are described. First, the mode is set to the normalobservation mode, and the insertion section 21 of the endoscope 12 isinserted into a body cavity. After the distal portion 24 of theinsertion section 21 reaches the stomach, the presence or absence of theatrophic gastritis is diagnosed. In a case where the color of the mucosais faded or a border (referred to as the endoscopic glandular border)between a site through which dendritic deep blood vessels are seen and asite through which the dendritic deep blood vessels cannot be seenappears in the normal light image, a doctor determines it as pathologicfindings (abnormal condition), being the emergence of a lesion e.g. thestomach cancer caused by the atrophic gastritis (a method for diagnosingbased on Kimura-Takemoto classification). Note that it has also beenknown that atrophy of gastric mucosa caused by infection of Helicobacterpylori leads to emergence of the stomach cancer.

In a case where the mucosa showing fading of color or the presence ofthe endoscopic glandular border cannot be found in the normal lightimage, the mode SW 22 b is operated to switch the mode to the specialobservation mode to diagnose more reliably. Upon switching the mode tothe special observation mode, the special light that includes both ofthe blue laser beams and the blue violet laser beams is emitted. Thefirst and second signal ratios are calculated based on the RGB imagesignals generated during the emission of the special light.

Based on the calculated first and second signal ratios, the averagevalue (the first area average value) of the first and second signalratios in the first area is calculated and this first area average valueis subjected to the polar coordinate conversion. The first and secondsignal ratios in each of the second to fifth areas are subjected to thepolar coordinate conversion. Thereby, the second to fifth area signalsthat have been subjected to the polar coordinate conversion aregenerated. The radial coordinate difference or the angular coordinatedifference between the first area average value, which has beensubjected to the polar coordinate conversion, and each of the second tofifth area signals, which have been subjected to the polar coordinateconversion, is expanded. Thereby the enhanced color difference signals(the enhanced second area signal, the enhanced third area signal, theenhanced fourth area signal, and the enhanced fifth area signal), inwhich the color difference between the normal mucosa and the abnormalregion is enhanced, are generated. The monitor 18 displays the speciallight image based on the enhanced color difference signal(s).

In a case where there is no atrophy of the stomach, the mucosa isdisplayed in its normal color in the special light image. In this case,a doctor determines it as normal findings with no lesion such as thestomach cancer caused by the atrophic gastritis. In a case where thereis a slight progress of the atrophy of the stomach, the atrophic mucosais displayed in faded colors and the deep blood vessels that are to beseen through the atrophic mucosa are displayed. Thereby the endoscopicglandular border is displayed clearly. A doctor is able to determine itas the pathologic findings where a lesion such as the stomach cancercaused by the atrophic gastritis is present even if the atrophic mucosashows little fading of color and not so many of the deep blood vesselsare seen through the mucosa in the actual stomach.

In the above embodiment, note that the special light including the bluenarrowband component (the blue laser beams and the blue violet laserbeams), to which the light absorbing material of the mucosa has highlight absorption properties, is used in the special observation mode, sothat the color differences among the atrophic mucosa, the deep bloodvessel region, and the BA region, which are in the abnormal region, andthe normal mucosal region in the observation area are greater than inthe case where the illumination light including the blue broadbandcomponent is used. The reason for this will be described below.

FIG. 12 illustrates the positions of the second to fifth areas in thetwo-dimensional space in a case where the special light including a bluenarrowband component (the blue laser beams and the blue violet laserbeams) is used in a manner similar to the above embodiment, and thepositions of the first to fifth areas in the two-dimensional space in acase where the illumination light including a blue broadband component(for example, 400 to 520 nm) is used. In FIG. 12, the second area Mn isobtained in a case where the special light including the blue narrowbandcomponent is used. The second area Mn represents an area that mostlycontains signals corresponding to the atrophic mucosa. The second areaMb is obtained in a case where the illumination light including the bluenarrowband component is used. The second area Mb represents an area thatmostly contains signals corresponding to the atrophic mucosa.

A third area Vn, a fourth area Xn, and a fifth area Yn are obtained in acase where the special light including the blue narrowband component isused. The third area Vn, the fourth area Xn, and the fifth area Ynrepresent an area that mostly contains signals corresponding to the deepblood vessel region, an area that mostly contains signals correspondingto the BA region, and an area that mostly contains signals correspondingto the redness region, respectively. A third area Vb, a fourth area Xb,and a fifth area Yb are obtained in a case where the special lightincluding the blue broadband component is used. The third area Vb, thefourth area Xb, and the fifth area Yb represent an area that mostlycontains signals corresponding to the deep blood vessel region, an areathat mostly contains signals corresponding to the BA region, and an areathat mostly contains signals corresponding to the redness region,respectively.

As illustrated in FIG. 12, the difference between the first area andeach of the second area Mn, the third area Vn, and the fourth area Xn islarge, whereas there is a little difference between the first area andeach of the second area Mb, the third area Vb, and the fourth area Xb.Thus, the difference between the first area and each of the second tofourth areas Mn, Vn, and Xn is increased sufficiently by using thespecial light including the blue narrowband component. In addition, thecolor difference enhancer 82 expands (increases) the radial coordinatedifference or the angular coordinate difference to further increase thedifference between the first area and each of the second to fourth areasMn, Vn, and Xn. Thus, the color difference between the normal mucosa andeach of the atrophic mucosal region, the deep blood vessel region, andthe BA region in the case where the special light including the bluenarrowband component is used is greater than in the case where theillumination light including the blue broadband component is used, bythe difference between the first area and each of the second to fourthareas Mn, Vn, and Xn caused by the blue narrowband component.

With respect to the fifth area Yn, as compared with the fifth area Yb,the difference between the fifth area Yn and the first area hardlydiffers from the difference between the fifth area Yb and the firstarea. Accordingly, the color difference between the normal mucosa andthe redness region does not vary much, regardless of using the speciallight including the blue narrowband component or the illumination lightincluding the blue broadband component.

As described above, the magnitude of the color difference between thenormal region and the abnormal region varies depending on whether thespecial light includes the blue narrowband component. This is mainly dueto factors that are dependent on the distribution density of the lightabsorbing material such as the blood density in the mucosa. This isexplained using the relationship (see FIG. 13) between the reflectiondensity, and the absorption coefficient (see FIG. 14 for thedistribution of the absorption coefficient of hemoglobin) and thedistribution density of the light absorbing material (mainly hemoglobinin digestive organ) in the mucosa. Note that, in a case where thereflection density is defined as “(−log (Bch) (the reflectance of thelight incident on the B ch of the image sensor))”, the first signalratio varies with a change in the reflection density.

According to FIG. 13, the reflection density increases nonlinearlyrelative to the absorption coefficient and the distribution density ofthe light absorbing material. The magnitude of the reflection densityincreases as the light absorption and the distribution density in themucosa increase. With regard to the increase in the amount of reflectiondensity, the reflection density increases significantly even with asmall increase in the absorption or the density in a case where thelight absorption is low and the distribution density is low, whereas thereflection density does not increase much with the increase in theabsorption or the density in a case where the light absorption is highand the distribution density is high.

Referring to the relationship of the distribution of the reflectiondensity illustrated in FIG. 13, the color difference between the normalmucosa and the abnormal region is described for each of the cases wherereflection light (hereinafter denoted as “narrowband light 445 nm+405nm”) of the mixed narrowband light of the blue laser beams (445 nm) andthe blue violet laser beams (405 nm), reflection light (hereinafterdenoted as “narrowband light 405 nm”) of the blue violet laser beams(405 nm), reflection light (hereinafter denoted as “narrowband light 445nm”) of the blue laser beams (445 nm), or reflection light (hereinafterdenoted as “broadband B light”) of the blue light in a broadbandwavelength range (for example, 400 to 500 nm) in a blue region isincident on the B ch of the image sensor 48.

Referring to the reflection density distribution in the BA regionillustrated in FIG. 15, the reflection density R1 of the narrowbandlight 405 nm is the highest. The reflection density R1 is followed bythe reflection density R2 of the narrowband light 445 nm+405 nm. Thereflection density R3 of the narrowband light 445 nm is lower than thereflection densities R1 and R2. The reflection density R4 of thebroadband B light is the lowest. This magnitude relationship is due tothe relationship among the magnitude of the light absorption “thenarrowband light 405 nm > the narrowband light 445 nm+405 nm > thenarrowband light 445 nm> the broadband B light” (see FIG. 14).

The difference between the reflection density R4 of the broadband Blight and each of the reflection densities R1 to R3 of the narrowband Blight (the narrowband light 405 nm, the narrowband light 445 nm+405 nm,and the narrowband light 445 nm) is relatively large. This is becausethe reflection density R4 of the broadband B light is especially low.The difference in reflection density between the normal mucosa and theBA region in the case where the narrowband B light is used is greaterthan in the case where the broadband B light is used. The reflectiondensity R4 of the broadband B light is low because the BA region isdistributed narrowly only in a relatively shallow location in the mucosa(see FIG. 16), so that the blood density along a light penetration pathis relatively low. In addition, the broadband B light includes thewavelengths around 500 nm, at which the absorption by the hemoglobin islow. The difference in reflection density (for example, the differencebetween the reflection density R1 and the reflection density R2) causedby the difference in wavelength of the narrowband B light is relativelylarger than in the case of the redness region. This is because the blooddensity along the light penetration path in the BA region is low, sothat the difference in light absorption caused by the difference inwavelength significantly influences the difference in reflectiondensity.

As illustrated in FIG. 17, the difference in the first signal ratiobetween the first area and the fourth area Xn in the case where thenarrowband Blight is used is greater than that between the first areaand the fourth area Xb in the case where the broadband B light is used,because the BA region has the above-described reflection density. In thecase where the positional relationship between the first area and eachof the fourth area Xn (405 nm) corresponding to the narrowband light 405nm, the fourth area Xn (445 nm+405 nm) corresponding to the narrowbandlight 445 nm+405 nm, and the fourth area Xn (445 nm) corresponding tothe narrowband light 445 nm, which are obtained by using the narrowbandB light, is compared with each other, the difference between the firstarea and the fourth area increases as the wavelength of the lightbecomes shorter. Thus, the difference between the first area and thefourth area is increased by using the narrowband B light. Accordingly,the color difference between the normal mucosal region and the BA regionis further increased.

Note that each of the blood densities along their light penetrationpaths in the atrophic mucosal region and the deep blood vessel region islower than that in the redness region, as in the case of the BA region.The atrophic mucosal region and the deep blood vessel region are similarto the BA region in reflection density distribution, so that thedifference between the first area and each of the second and third areasis increased by using the light of shorter wavelengths, as in the caseof the BA region. Thus, the difference between the first area and eachof the second and third areas is increased by using the narrowband Blight. Accordingly, the color difference between the normal mucosalregion and each of the atrophic mucosal region and the deep blood vesselregion is further increased.

As illustrated in FIG. 18, the magnitude relationship among thereflection densities R1 to R4 in the redness region is similar to thatin the BA region or the like. However, the difference between thereflection density R4 of the broadband B light and each of thereflection densities R1 to R3 of the narrowband B light is relativelysmaller than in the case of the BA region or the like. This is becausethe reflection density R4 of the broadband B light is higher than thatin the BA region or the like. The reflection density R4 of the broadbandB light is relatively high because the redness is widely distributedfrom shallow to deep locations in the mucosa as illustrated in FIG. 19,so that the blood density along the light penetration path is relativelyhigh.

With regard to the narrowband B light, the difference in reflectiondensity (for example, the difference between the reflection density R1and the reflection density R2) caused by a difference in wavelength isnot so large as compared with that in the BA region. This is because theblood density in the redness region along the light penetration path isrelatively high as compared with that in the BA region or the like. Thedifference in wavelength may cause a difference in light absorption butit has a limited influence on the difference in reflection density.

As illustrated in FIG. 20, because the redness region has theabove-described reflection density, the difference between the firstarea and the fifth area Yn in the case where the narrowband B light isused does not differ much from the difference between the first area andthe redness region Yb in the case where the broadband B light is used.With regard to the cases where the narrowband B light is used, thepositional relationship between the first area and each of the fiftharea Yn (405 nm) corresponding to the narrowband light 405 nm, the fiftharea Yn (445 nm+405 nm) corresponding to the narrowband light 445 nm+405nm, and the fifth area Yn (445 nm) corresponding to the narrowband light445 nm is compared with each other. There is little difference betweenthe first area and each of the fifth areas. Thus, the narrowband B lightdoes not increase the difference between the first area and the fiftharea much. Accordingly, the color difference between the normal mucosalregion and the redness region is not increased much.

However, in a case where the redness region is of a mild level (mildredness region) and not a high blood density region such as advancedredness or bleeding, the difference in reflection density between thenormal mucosal region and the mild redness region in the case where thenarrowband B light is used is greater than in the case where thebroadband B light is used. Accordingly, the color difference between thenormal region and the mild redness region is increased by using thenarrowband B light.

The above describes the change in the first signal ratio in the casewhere the wavelength range of the B light to be incident on the B ch ofthe image sensor 48 is narrowed (that is, the positions of the second tofifth areas shift in the vertical axis direction in the two-dimensionalspace in the case where the wavelength is narrowed). Note that a casewhere the wavelength range of the G light to be incident on the G ch ofthe image sensor 48 is narrowed is described in a like manner. In thecase where the narrowband G light (the G light of the wavelengths atwhich a high amount of the G light is absorbed by blood) is used, thedifference between the first and second areas is larger than in the casewhere the broadband G light is used (the second to fifth areas shift inthe horizontal axis direction in the case where the wavelength range isnarrowed).

In the above description, the wavelength range of one of the B light tobe incident on the B ch of the image sensor 48 and the G light to beincident on the G ch of the image sensor 48 is narrowed. Note that thewavelength ranges of both the B light and the G light may be narrowedinstead. In this case, as a result of narrowing the wavelength ranges,the second to fifth areas shift in the vertical axis direction and thehorizontal axis direction in the two-dimensional space. However, theamount of the shift in the vertical axis direction is smaller than inthe case where only the wavelength range of the B light to be incidenton the B ch of the image sensor 48 is narrowed. This is because both theabsorption coefficient for the B ch and the absorption coefficient forthe G ch are increased by the narrowband B light and the narrowband Glight. Therefore the difference between the reflection density of the Bch and the reflection density of the G ch is smaller than in the casewhere only the wavelength range for the B ch is narrowed.

In the above embodiment, the polar coordinate conversion is performed onthe first and second signal ratios. The radial coordinate difference orthe angular coordinate difference between the first area average valuethat has been subjected to the polar coordinate conversion and thesignal value in each of the second to fifth areas that has beensubjected to the polar coordinate conversion is expanded. Thereby thedifference in color between the normal mucosal region and the abnormalregion is enhanced. Another coordinate conversion method and anothercolor difference enhancement method may be used to enhance thedifference in color between the normal mucosal region and the abnormalregion. Note that, in the case where the enhanced image is produced byusing the color difference enhancement method for expanding the radialcoordinate difference or the angular coordinate difference in the polarcoordinate system as described in the above embodiment, the color of thenormal mucosal region in the enhanced image is the same as that of thenormal mucosal region in the normal light image, so that the enhancedimage looks natural. The colors of the atrophic mucosal region and thedeep blood vessel region in the enhanced image are the same as theactual colors of the atrophic mucosa with the atrophic gastritis and theblood vessels seen through the atrophic mucosa, so that a method similarto the currently used method (for example, ABC screening) may be usedfor diagnosing the atrophic gastritis.

In the above embodiment, the first area average value is used to enhancethe color difference between the normal mucosal region and the abnormalregion. Note that the average value of the pixel values of the entireimage signal may be used instead. In this case, although the color ofthe atrophic mucosa and the color of the deep blood vessels may vary onan image-by-image basis, there is a merit that a slight differencebetween the normal mucosal region and the abnormal region is expanded inaccordance with the distribution of each region in the image.

In the above embodiment, the first and second signal ratios aresubjected to the polar coordinate conversion. The expansion process forexpanding the radial coordinate difference or the angular coordinatedifference is performed on the signal that has been subjected to thepolar coordinate conversion. Note that the polar coordinate conversionprocess and the expansion process may be performed in advance and theresults of the processes may be stored in a LUT (lookup table) for colordifference enhancement. In this case, the first and second signal ratiosthat are considered to be in the second to fifth areas are calculatedusing the above-described expressions (1) to (6) in advance. The firstand second signal ratios in each of the second to fifth areas and thecorresponding results of the calculations using the first and secondsignal ratios are associated with each other and stored in the LUT forcolor difference enhancement. The first and second signal ratios thatare considered to be in the first area are associated with the valuesidentical thereto and stored in the LUT for color differenceenhancement. With the use of the LUT for color difference enhancement,the color difference between the normal mucosal region and the abnormalregion is enhanced without the polar coordinate conversion process andthe expansion process. Thus a processing load is reduced.

In the above embodiment, the color difference enhancer 82 performs thecolor difference enhancement process for enhancing the color differencebetween the abnormal region and the normal region. Note that, with theuse of the special light including the blue narrowband component (theblue laser beams and the blue violet laser beams), to which the lightabsorbing material of the mucosa has high absorption properties, thecolor difference between the normal mucosal region and the abnormalregion (the atrophic mucosal region, the deep blood vessel region, theBA region, or the redness region) is enhanced and displayed without thecolor difference enhancement process, which is performed by the colordifference enhancer 82. In a like manner, with the use of lightincluding a green narrowband component (for example, a wavelengthcomponent of 540 to 560 nm), to which the light absorbing material ofthe mucosa has high light absorption properties, the color differencebetween the normal mucosal region and the abnormal region (the atrophicmucosal region, the deep blood vessel region, the BA region, or theredness region) is enhanced and displayed without the color differenceenhancement process performed by the color difference enhancer 82.

Note that, in the first embodiment, the phosphor 44 is provided in thedistal portion 24 of the endoscope 12. Instead, the phosphor 44 may beprovided in the light source device 14. In this case, it is preferred toprovide the phosphor 44 between the light guide 41 and the blue laser34.

Second Embodiment

In the first embodiment, the RGB image signals are generatedsimultaneously by the color image sensor. In a second embodiment, theRGB image signals are generated sequentially by a monochrome imagesensor. As illustrated in FIG. 21, the light source device 14 of anendoscope system 200 of the second embodiment comprises a broadbandlight source 202, a rotary filter 204, and a filter switcher 205,instead of the blue laser 34, the blue violet laser 36, and the sourcecontroller 40. The illumination optical system 24 a of the endoscope 12eliminates the phosphor 44. The imaging optical system 24 b is providedwith a monochrome image sensor 206, which eliminates the color filters,in place of the color image sensor 48. Other than those, the endoscopesystem 200 is similar to the endoscope system 10 of the firstembodiment.

The broadband light source 202 comprises a xenon lamp, a white LED, orthe like, and emits white light in the wavelength range from blue tored. The rotary filter 204 comprises a normal observation mode filter208 provided on an inner side and a special observation mode filter 209provided on an outer side (see FIG. 22). The filter switcher 205 shiftsthe rotary filter 204 in a radial direction. In a case where the mode isset to the normal observation mode by operating the mode SW 22 b, thefilter switcher 205 inserts the normal observation mode filter 208 ofthe rotary filter 204 into the light path of the white light. In a casewhere the mode is set to the special observation mode, the filterswitcher 205 inserts the special observation mode filter 209 of therotary filter 204 into the light path of the white light.

As illustrated in FIG. 22, the normal observation mode filter 208comprises a B filter 208 a, a G filter 208 b, and an R filter 208 c in acircumferential direction. The B filter 208 a transmits blue light ofthe white light. The G filter 208 b transmits green light of the whitelight. The R filter 208 c transmits red light of the white light. In thenormal observation mode, the blue light, the green light, and the redlight are applied in this order to the object as the rotary filter 204is rotated.

The special observation mode filter 209 comprises a Bn filter 209 a, a Gfilter 209 b, and an R filter 209 c in the circumferential direction.The Bn filter 209 a transmits blue narrowband light having the centerwavelength of 415 nm of the white light. The G filter 209 b transmitsgreen light of the white light. The R filter 209 c transmits red lightof the white light. In the special observation mode, the blue narrowbandlight, the green light, and the red light are applied in this order tothe object as the rotary filter 204 is rotated.

In the normal observation mode, the monochrome image sensor 206 of theendoscope system 200 captures an image of the object every time the bluelight, the green light, or the red light is applied to the object.Thereby, image signals of the three colors (RGB) are generated. Thenormal light image is produced based on the RGB image signals by amethod similar to that in the first embodiment.

In the special observation mode, the monochrome image sensor 206captures an image of the object every time the blue narrowband light,the green light, or the red light is applied to the object. Thereby, aBn image signal, a G image signal, and an R image signal are generated.The special light image is produced based on the Bn image signal, the Gimage signal, and the R image signal. The Bn image signal is used inplace of the B image signal to produce the special light image. Otherthan that, the special light image is produced by a method similar tothat of the first embodiment.

Third Embodiment

The endoscope system 10 of the first embodiment uses the B image signal,being the narrowband signal containing narrowband wavelength informationof the blue laser beams and the blue violet laser beams, to produce thespecial light image. The endoscope system 200 of the second embodimentuses the Bn image signal, being the narrowband signal containing thenarrowband wavelength information of the blue narrowband light, toproduce the special light image. In a third embodiment, a bluenarrowband image signal is generated by spectral calculation based on abroadband image such as a white light image. Based on the bluenarrowband image signal, the special light image is produced.

In the special observation mode of the synchronization-type endoscopesystem 10 in the third embodiment, white light, being the broadbandlight, is emitted instead of the special light. As illustrated in FIG.23, a spectral calculator 300, which is disposed between the receiver 54and the inverse gamma converter 76, performs a spectral calculationprocess based on the RGB image signals generated by imaging the objectirradiated with the white light. Thereby the blue narrowband imagesignal is generated. The spectral calculation method described inJapanese Unexamined Patent Application Publication No. 2003-093336 isused. The special light image is generated, in a manner similar to thefirst embodiment, based on the blue narrowband image signal generated bythe spectral calculator 300, the G image signal, and the R image signal.Note that the white light obtained using the phosphor 44, the broadbandlight emitted from a broadband light source such as the xenon lamp, orthe like may be used as the white light.

The above embodiments describe an example in which the color of themucosa is faded due to the atrophic gastritis and an example in whichthe deep blood vessels located beneath the atrophic mucosa are seenthrough the atrophic mucosa. Note that the color of the mucosa may befaded due to a lesion of another site (for example, a lesion inesophagus or a lesion in large intestine). The present invention alsoenables enhancing the color difference between the normal region andmucosa, other than the above-described atrophic mucosa, showing fadingof color. The present invention also enables enhancing and displayingthe deep blood vessels located beneath and seen through the mucosa,other than the atrophic mucosa, showing fading of color.

Note that the above-described first to fourth expansion processesincrease the color difference between the abnormal region (the atrophicmucosa, the deep blood vessels, the BA, or the redness) and the normalmucosa while the color of the normal mucosa is maintained unchanged.According to the above embodiments, an image in which the color of thenormal mucosa is maintained unchanged is displayed after any of thefirst, second, third, and fourth expansion processes.

It is necessary to perform the first, second, third, or fourth expansionprocess as follows to display the image in which the color of the normalmucosa is maintained unchanged as described above. For example, in thefirst expansion process, the third expansion process, and the fourthexpansion process, in which a radial coordinate is expanded, the radialcoordinate r that is within the first area is converted into the radialcoordinate Er that is equivalent to the radial coordinate r (identicaltransformation) (see FIG. 26) in a case where the first area is definedto be in a range from “rm−Δr1” to “rm+Δr2” (see FIG. 24). For example,the radial coordinate Er is “rm” in a case where the radial coordinate ris “rm”. After the first, third, or fourth expansion process, the colorof the normal mucosa is maintained unchanged in the image by theidentical transformation of the radial coordinate r that is located inthe first area.

As illustrated in FIG. 24, the radial coordinate ri (of the second area)smaller than the first area average value rm is converted into theradial coordinate Eri smaller than the radial coordinate ri (see FIG.26). As illustrated in FIG. 25, the radial coordinates rk and rj (of thefourth and fifth areas), which are greater than the first area averagevalue rm in most cases, are converted into the radial coordinates Erkand Erj, which are greater than the radial coordinates rk and rj. FIG.26 illustrates the correspondence between the radial coordinate r andthe radial coordinate Er within an angular coordinate θ of apredetermined range that includes the first to fifth areas. Note that adifferent correspondence may be set for each angular coordinate θ.

In the second expansion process, the third expansion process, and thefourth expansion process, in which the angular coordinate is expanded,the angular coordinate θ that is within the first area is converted intothe angular coordinate Eθ that is equivalent to the angular coordinate θ(identical transformation) (see FIG. 29) in a case where the first areais defined to be in a range from “θm−Δθ1” to “θm+Δθ2” (see FIG. 27). Forexample, the angular coordinate Eθ is “θm” in a case where the angularcoordinate θ is “θm”. Thus, after the second, third, or fourth expansionprocess, the color of the normal mucosa is maintained unchanged in theimage by the identical transformation of the angular coordinate θ thatis located in the first area.

As illustrated in FIG. 27, the angular coordinate θv (of the third area)smaller than the first area average value 8m is converted into theangular coordinate Eθv smaller than the angular coordinate θv (see FIG.29). As illustrated in FIG. 28, the angular coordinate θk (of the fourtharea), which is greater than the first area average value θm in mostcases, is converted into the angular coordinate Eθk, which is greaterthan the angular coordinate θk (see FIG. 29). As illustrated in FIG. 28,the angular coordinate θj (of the fifth area), which is smaller than thefirst area average value θm in most cases, is converted into the angularcoordinate Eθj, which is smaller than the angular coordinate θj (seeFIG. 29). Note that, in FIG. 29, “θm” denotes an angle defined to bewithin a range from 0° to 90°. “θm−90” denotes a negative angle. “θm+90”denotes a positive angle. An angle increases toward the right on thehorizontal axis. The angle increases toward the upper end of thevertical axis.

In the above embodiments, the implementation of the present invention isperformed during the diagnosis using the endoscope, but not limitedthereto. Note that the implementation of the present invention may beperformed after the diagnostic endoscopy, based on an endoscopic imagestored in a storage unit of the endoscope system. The implementation ofthe present invention may be performed based on a capsule-endoscopicimage captured with a capsule endoscope.

Various changes and modifications are possible in the present inventionand may be understood to be within the present invention.

What is claimed is:
 1. An image processing device comprising: an imagesignal inputting unit for inputting image signals of three colors; asignal ratio calculator for calculating a first signal ratio between theimage signals of two colors and a second signal ratio between the imagesignals of two colors different from the first signal ratio, based onthe image signals of three colors; a color difference enhancer forperforming a first expansion process, the first expansion processexpanding a difference between first and second signal ratios in a firstarea and first and second signal ratios in a second area different fromthe first area; and a display unit for displaying an image in which acolor difference between normal mucosa and a first abnormal region on anobject of interest is enhanced based on the first and second signalratios subjected to the first expansion process.
 2. The image processingdevice according to claim 1, wherein the first expansion process is aprocess for expanding a radial coordinate difference between the firstand second signal ratios in the first area and the first and secondsignal ratios in the second area.
 3. The image processing deviceaccording to claim 2, wherein the process for expanding the radialcoordinate difference is performed based on a signal obtained by polarcoordinate conversion of the first and second signal ratios in the firstarea and a signal obtained by polar coordinate conversion of the firstand second signal ratios in the second area.
 4. The image processingdevice according to claim 1, wherein saturation of the first abnormalregion is reduced by the first expansion process.
 5. The imageprocessing device according to claim 1, wherein the first abnormalregion is mucosa showing fading of color, including atrophic mucosa. 6.The image processing device according to claim 1, wherein the firstexpansion process expands the difference between the first and secondsignal ratios in the first area and the first and second signal ratiosin the second area while the first and second signal ratios in the firstarea are maintained unchanged, and the display unit displays an image inwhich a color of the normal mucosa is maintained unchanged.
 7. The imageprocessing device according to claim 1, wherein the color differenceenhancer performs a second expansion process in addition to the firstexpansion process, the second expansion process expanding a differencebetween the first and second signal ratios in the first area and firstand second signal ratios in a third area different from the first andsecond areas, and the display unit displays an image in which the colordifference between the normal mucosa and the first abnormal region onthe object of interest and a color difference between the normal mucosaand a second abnormal region on the object of interest are enhanced. 8.The image processing device according to claim 7, wherein the secondexpansion process is a process for expanding an angular coordinatedifference between the first and second signal ratios in the first areaand the first and second signal ratios in the third area.
 9. The imageprocessing device according to claim 8, wherein the process forexpanding the angular coordinate difference is performed based on asignal obtained by polar coordinate conversion of the first and secondsignal ratios in the first area and a signal obtained by polarcoordinate conversion of the first and second signal ratios in the thirdarea.
 10. The image processing device according to claim 7, wherein thesecond abnormal region is located beneath the first abnormal region, andhue of the second abnormal region is changed by the second expansionprocess, so that blood vessels beneath the first abnormal region areseen through the first abnormal region.
 11. The image processing deviceaccording to claim 7, wherein the second expansion process expands thedifference between the first and second signal ratios in the first areaand the first and second signal ratios in the third area while the firstand second signal ratios in the first area are maintained unchanged, andthe display unit displays an image in which a color of the normal mucosais maintained unchanged.
 12. The image processing device according toclaim 7, further comprising an average value calculator for calculatingan average value of the first and second signal ratios in the firstarea, wherein the color difference enhancer expands a difference betweenthe average value and the first and second signal ratios in the secondarea and expands a difference between the average value and the firstand second signal ratios in the third area.
 13. The image processingdevice according to claim 7, wherein a suppression process for reducingthe enhancement of the color difference is performed in a high luminancearea or a low luminance area in the first to third areas.
 14. The imageprocessing device according to claim 1, wherein the first signal ratiois a B/G ratio between a B image signal and a G image signal, and thesecond signal ratio is a G/R ratio between the G image signal and an Rimage signal.
 15. A method for operating an endoscope system comprisingthe steps of: inputting image signals of three colors with an imagesignal inputting unit; calculating a first signal ratio between theimage signals of two colors and a second signal ratio between the imagesignals of two colors different from the first signal ratio, based onthe image signals of three colors with a signal ratio calculator;performing a first expansion process with a color difference enhancer,the first expansion process expanding a difference between first andsecond signal ratios in a first area and first and second signal ratiosin a second area different from the first area; and displaying an imagein which a color difference between normal mucosa and a first abnormalregion on an object of interest is enhanced based on the first andsecond signal ratios subjected to the first expansion process, on adisplay unit.